Dorsal Stabilization of a C3–C4 Vertebral Luxation and Cervical Facet Dislocation in a German Shepherd Dog

Abstract

Locked facet injury is a possible severe consequence of trauma in companion animals and occurs predominantly in small and toy breed dogs. Stabilization of the cervical vertebral column is traditionally described via a ventral approach, whereas reduction of luxation is better achieved via a dorsal approach. This report describes a 3-year-old, female spayed German Shepherd dog that presented for tetraplegia caused by a presumptive road traffic accident. Clinical examination and diagnostic imaging revealed a dorsal subluxation of the C4 vertebra at the C3–C4 junction, with a right-sided locked facet injury. Luxation reduction and stabilization were achieved with a dorsal approach and internal fixation with screws in the articular process joints of C3–C4 and the pedicles of C3 and C4. Long-term follow-up showed complete recovery of ambulation and return to an active life-style

Keywords

dorsal vertebral stabilization - spinal surgery - dog - locked facet injury

Introduction

The articular process joints are complex biomechanical structures that play an important role in the stability of the cervical vertebral column and its dynamic involvement in posture and gait.[1] Luxation of the cervical articular process joints has been reported in dogs as “cervical facet dislocation” (unilateral or bilateral), cervical “locked facet injury,” or “subaxial cervical articular process subluxation.”[2] In humans, locked facet injuries are associated with rotationally unstable cervical spine injuries, and treatment options include both anterior and posterior stabilization, as well as closed reduction techniques.[3]

Locked facet injury in companion animals occurs predominantly in small and toy breed dogs. In dogs, a ventral approach is commonly recommended for the reduction and stabilization of the cervical vertebral column, while a dorsal approach is discouraged due to the sparse bone available for implant placement and because of postoperative morbidity.[4] [5] [6] [7] However, there is lack of original studies in the literature to objectively compare the biomechanical properties and clinical outcomes of both approaches and stabilization techniques of the canine cervical spine. Except for atlantoaxial luxation, dorsal stabilization of the cervical vertebral column is uncommonly reported, and has not been reported as a sole stabilization technique for C3–C4 luxation. Dorsal approach to the cervical vertebral column has been reported as a first step in a multi-stage surgery for dorsal reduction of luxation, followed by subsequent ventral stabilization,[2] in combination with ventral stabilization for a C2 fracture,[8] or to stabilize a C6 fracture via transarticular screws.[9] There are no reports of C3–C4 locked facet injuries in large breed dogs, nor documentation of their surgical management using a dorsal approach and stabilization. The purpose of this case report is to describe the diagnosis, stabilization technique, and follow-up of a C3–C4 locked facet injury in a large breed dog.

Case Report

A 3-year-old, female spayed German Shepherd dog was referred to the Veterinary Medical Teaching Hospital (VMTH) at the University of California Davis for assessment, after being found laterally recumbent on the side of the road. On physical examination, blood was present in the oral cavity secondary to oral wounds. On neurological examination, the dog was laterally recumbent and tetraplegic with intact superficial pain sensation in all four limbs. No movement of head or neck was noted, and the dog was unable to get into a sternal position. Spinal reflexes were normal in all four limbs and the cutaneous trunci reflex was present to the level of the iliac wing bilaterally. Although no voluntary urination was observed, the bladder was palpated as soft. The neuroanatomical localization was a C1–C5 myelopathy, with a traumatic cause considered most likely.

A complete blood count and serum biochemistry panel done by the referring veterinarian were normal except for an increased hematocrit of 59%. Referral radiographs (see [Fig. 1]) showed a C3–C4 dorsal subluxation with severe narrowing of the vertebral canal. At the VMTH, a computed tomography (CT) of the cervical vertebral column was performed. The patient was strapped to a backboard, sedated with hydromorphone (Hydromorphone Hydrochloride Injection USP; West-Ward Pharmaceutical Corp., NJ, USA)[a] 0.05 mg/kg IV and dexmedetomidine (dexmedetomidine hydrochloride, Dexdomitor; Zoetis, Troy Hills, NJ, USA)[b] 5 ug/kg IV for CT examination. Preoperative CT was performed with a Lightspeed 16 helical scanner (General Electric Co, Milwaukee, WI, USA)[c]. The scan was performed with acquisition parameters of 120 kVp, 180 mA, and 0.625 mm image thickness in a bone algorithm. The patient was imaged from the level of the temporomandibular joints to T1. Findings from the CT examination included dorsal subluxation and rightward rotation of the C4 vertebral body relative to C3 with complete luxation of the right C3–C4 articular process joint, consistent with locked facet injury ([Figs. 1] and [2]), and mild subluxation of the left C3–C4 articular process joint ([Fig. 1]). There was a fracture at the most caudal tip of the right caudal articular process of C3, as well as a fracture through the entire right transverse process of C4. The dog was kept in lateral recumbency overnight on a cushioned backboard, with thick blankets to prevent bedsores, in preparation for surgery the following day.

Fig. 1 (A) Left lateral cervical radiograph. Note the misalignment of the vertebral bodies at C3–C4 (arrow) and narrowing of the vertebral canal at this level. (B) Left lateral midsagittal preoperative CT of the cervical spine showing dorsal subluxation at C3–C4 (arrow). (C) Transverse CT image at the level of the C3–C4 joint showing rightward rotation of the C3 vertebral body relative to C4 with complete luxation of the right cranial articular process of C4 (†) dorsal to the caudal articular process of C3 (‡), consistent with locked facets of the right C3–C4 articular process joint (white arrow) and mild subluxation of the left C3–C4 articular process joint (yellow arrow). Note the fractures of the C3 right caudal articular process and transverse process of C4 (asterisk).

Fig. 2 Three-dimensional reconstruction of the CT scan of the cervical spine of the dog with a right C3–C4 locked facet injury (arrow in A [right lateral] and B [dorsal]). For comparison, the same reconstruction in a normal dog with physiologic apposition of the right C3–C4 facets (arrow in C [right lateral] and D [dorsal]).

Presurgical planning included: (1) consideration for luxation reduction, which was thought to be optimized by direct visualization of the locked facets, leading to the decision to opt for a dorsal approach; (2) identification of safe corridors to optimize pedicle bone purchase ([Fig. 3]); (3) minimizing the risk of vertebral artery laceration by pre-measuring all anticipated trajectories and preparing adequately sized implants.

Fig. 3 Surgical planning: evaluation of safe corridor for pedicle screw placement. The pedicle lies under the small ridge on the dorsal aspect of the vertebral body. The pedicle is thickest at the level of the mid vertebral body, between the cranial and caudal articular facets. (A) Dorsal view. (B) Transverse and caudal view. (C) Lateral view. (D) Dorsolateral view. The dashed line follows the direction of the ridge that can be palpated intraoperatively to visualize pedicles. Note that this is also the trajectory the transverse foramen is expected to follow. Presurgical measurement is paramount to prevent violation of this canal. The dotted line marks the cranial and caudal extent of the thickest part of the pedicle. The screws should ideally be placed along the dashed lines between the dotted lines.

The dog was premedicated with methadone (Methadone Hydrochloride; Akorn, Inc, Lake Forest, IL, USA)[d] 0.2 mg/kg IV. General anesthesia was induced with midazolam (Midazolam Hydrochloride, Versed; Hospira, Lake Forest, IL, USA)[e] 0.3 mg/kg IV and ketamine (Ketamine Hydrochloride; Fort Dodge Animal Health, Fort Dodge, IA, USA)[f] 4 mg/kg IV and maintained with a gas mixture of isoflurane (Isoflurane USP, IsoFlo; Abbott Laboratories, IL, USA)[g] and oxygen. Analgesia was provided using a constant rate infusion of fentanyl (Fentanyl Citrate USP; Pfizer, NY, USA)[h] (0.005–0.008 mg/kg/h IV), ketamine (30 mcg/kg/min IV), and cefazolin (Cefazolin; Westward Pharmaceutical, Eatontown, NJ, USA)[i] (22 mg/kg IV) which was given after induction and every 2 hours until closure of the skin was completed.

For surgery, the dog was positioned in sternal recumbency, maintained with a vacuum-activated positioning system. The head was mildly flexed ventrally over a rolled towel and maintained in a straight position by securing the canine to the table with tape. A dorsal midline approach was performed as previously described.[10] Fracture of the caudal tip of the right caudal articular process of C3 was noted and the free fragment was removed with forceps. Muscle relaxation was accomplished using rocuronium (Rocuronium Bromide, Zemuron; Merck & Co. Inc., NJ, USA)[j] 0.2 mg/kg IV to assist in reduction of the luxation while the patient was maintained under mechanical ventilation, and no reversal was used due to the short duration of action. Bone reduction forceps were positioned over the spinous processes of C3 and C4 to facilitate traction in cranial and caudal directions, respectively, which allowed reduction of the luxation. Two 28 × 2.0 mm transarticular screws (Jorgensen Laboratories, LLC, Loveland, CO, USA)[k] were inserted through the C3–C4 articular process joints bilaterally. On the right side, the transarticular screw was inserted rostral to fracture site, which involved only the caudal tip of the C3 right caudal articular process. Two 22 × 2.0 mm and two 18 × 2.0 mm diameter pedicle screws were placed through C4 bilaterally, respectively, at the caudal third and cranial third of the vertebral body length. Three 16 × 2.0 mm diameter pedicle screws were placed in the caudal aspect of C3, one on the right side and two engaging the left side. Holes were pre-drilled with a 1.5-mm drill bit and their depth was measured. Approximately 5 to 10 mm of the screw heads were left exposed dorsal to the vertebral body for stabilization with polymethylmethacrylate (PMMA; Surgical Simplex P; Stryker, Portage, MIm USA )[l]. The surgical site was flushed with saline while the PMMA was cured. The surgical incision was closed routinely. A bandage was applied over the incision site (Primapore; Smith & Nephew plc; Watford, United Kingdom )[m].

Postoperatively, CT was performed with acquisition parameters of 120 kVp, 150 mA, and 0.625 mm image thickness in a bone algorithm, imaged from C1 to C6. Postoperative radiographs and CT ([Fig. 4]) confirmed reduction of the luxation facet dislocation, and adequate positioning of the screws.

Fig. 4 Postoperative left lateral (A) and dorsoventral (B) radiographs of the cervical spine and transverse cross-sectional images (C–H) showing implant positioning, postoperative reduction, and internal fixation of the C3–C4 left articular process joint luxation with resolved rotational malalignment. (A, B) Reduction and stabilization of the patient's C3–C4 articular process fracture/luxation with good alignment of C3–C4. Implants include radiopaque PMMA overlying the C3–C4 articular process joints bilaterally and nine associated screws. There are three screws engaging the right caudal aspect of C3 and two screws engaging the left caudal aspect of C3. There are two screws engaging the right cranial aspect of C4 and two screws engaging the left mid to caudal aspect of C4. (C–H) The luxated left C3–C4 articular process joint is reduced and there is no longer rotation of C4 relative to C3. Screws were placed through the caudal articular processes of C3 (C), both parts of the C3–C4 articular process joints bilaterally (D, E), and the pedicle of C4 bilaterally (F, H). The heads of all these screws terminate in the PMMA.

Post-surgery, the dog showed progressive neurological recovery. By day 1, voluntary motor function returned in the thoracic limbs, and by day 3, all four limbs showed voluntary movement with the ability to maintain sternal recumbency briefly. On day 5, the dog was non-ambulatory tetraparetic with improved motor in the left thoracic and pelvic limbs, and could walk with a harness. Continued motor improvement and the ability to urinate voluntarily allowed discharge on day 7.

At the first follow-up neurological examination 7 weeks after surgery, the patient was ambulatory tetraparetic with mild to moderate ataxia, long-strided gait, particularly in the thoracic limbs, and no pain on cervical palpation/manipulation. Long-term follow-up up to 2 years postoperatively revealed full ambulation and return to an active lifestyle.

Discussion

The facet joints act as dorsal stabilizers of the vertebral column during rotation, and their integrity is most compromised during flexion, when the support provided by the facets is significantly reduced.[1] [11] Therefore, during trauma causing compression flexion of the cervical vertebral column, luxation of these facet joints may occur, causing locket facet injury.[12] This condition is primarily reported in small and toy breed dogs.[2]

Neurological and radiographic examination are essential for evaluation of cervical trauma. Compared with radiography, CT has better spatial resolution for the evaluation of articular process luxation. Although the diagnosis of vertebral luxation can be achieved with radiographs, cross-sectional views are required for evaluation of the rotational component. An in-depth knowledge of the anatomy of the cervical spine vertebrae, together with review of the cross-sectional imaging, allows adequate surgical planning. Whereas MRI provides excellent images for diagnosis of spinal cord intrinsic lesions, CT yielded outstanding preoperative evaluation of the anatomy for surgical planning and was adequate in this case.

A dorsal approach to the cervical spine was ideal for evaluation, reduction, and stabilization of the C3–C4 luxation. Moreover, a dorsal approach was required to ensure adequate reduction of the luxation. Therefore, the combined reduction and stabilization via the same approach significantly reduced the operative time and eased manipulation of the unstable cervical spine, and prevented the need for an additional surgical site. Furthermore, the use of cortical screws allowed adequate bone purchase without violation of the vertebral canal or trauma to the vascular structures of the cervical spine, including the vertebral artery in the transverse foramen.

In this large breed dog, the physical reduction of the luxation was the major difficulty encountered, requiring traction of cervical vertebrae in opposite direction against the tensile forces from robust cervical musculature. Reduction was facilitated by chemical relaxation of the patient using a non-depolarizing neuromuscular blocker (rocuronium).

There is a risk of vertebral artery laceration during cervical pedicle drilling, and safe corridors in dogs have been described only for ventral stabilization.[13] The surgery planning for this patient, together with the preoperative imaging, allowed for description of safe corridors for instrumentalization of the C3 and C4 vertebrae from a dorsal approach. Although not used in the management of this case, the use of drill stop may help prevent accidental laceration of the vertebral artery. Furthermore, the use of patient-specific 3D-printed drill guides has shown promising results in cadaveric studies to optimize the accuracy of cervical pedicle screw placement.[14] Previously documented limitations of a dorsal approach for instrumentalization of the cervical spine include inability to achieve sufficient bone coverage without violation of the vertebral canal, with sparse bone available for implants[4] and extensive muscle dissection resulting in postoperative morbidity.[6] The small size of the cervical vertebrae pedicles and the presence of transverse foramina housing the vertebral arteries have discouraged the use of dorsal approach for safe implant position.[6] For this case, cross-sectional images allowed preoperative measurements to adequately evaluate safe screw size and to prevent laceration of the vertebral artery, a potentially life-threatening complication.

The dorsal approach resulted in excellent reduction, appropriate visualization to secure pedicle screws, good stability of the reduced luxation, functional range of motion of the cervical spine, and minimal signs of pain in the postoperative period. Other advantages of a dorsal approach include avoiding the vital structures present on the ventral cervical area including carotid artery, vagosympathetic trunk, recurrent laryngeal nerve, and the transverse foramen and vertebral artery that could be damaged during a ventral approach, dissection, manipulation, or instrumentalization of the ventral cervical spinal cord.

These considerations are in line with the surgical indications for a posterior approach in people, where cervical facet injuries, such as fractures or locked facets, are amenable to posterior stabilization procedures.[15] In these cases, deformity reduction, decompression, fixation, and fusion can all be performed in the same procedure. In people, this can be accomplished by manually reducing the misaligned facets or by facetectomy if manual reduction is not feasible. Other advantages of this approach described in the human literature include the ease of exploration of the canal or foramen and the ability to remove fractured bone fragments through laminectomy or facetectomy, which may compress the spinal cord or nerve root.[16] Cervical pedicle screws demonstrate a higher resistance than lateral mass screws, thus providing posterior stabilization with a substantial biomechanical advantage in people.[17] In addition, surgical complications associated with dorsal pedicle screw fixations are reportedly low in people, but may include hemorrhage from the vertebral artery and radiculopathy caused by foraminal stenosis.[18] It is worth noting that these complications can be encountered with many different methods of instrumentalization of the cervical spine and surgical approaches. A large systematic review of the literature comparing anterior versus posterior stabilization of the cervical spine in people did not identify robust difference in the long-term neurological status.[19] In this review, only patients who underwent an anterior approach developed postoperative swallowing disorders.[19]

In this case, a dorsal approach was elected to optimize direct visualization of the locked facet and guide intraoperative reduction. Cranial and caudal traction of the C3 and C4 vertebrae, respectively, was required, along with rotation of the bones in relation to one another. In small dogs, reduction can be performed via a ventral approach. Transarticular screws maintained reduction during placement of pedicle screws in both C3 and C4 vertebrae, which provided solid bone purchase. Further cases are required to determine whether this approach is optimal for repair of locked facet joint in dogs and if large breed dogs are better surgical candidates.

Conflict of Interest

None declared.

^a Hydromorphone Hydrochloride Injection USP; West-Ward Pharmaceutical Corp., NJ, USA.

^b Dexmedetomidine hydrochloride, Dexdomitor; Zoetis, Troy Hills, NJ, USA.

^c General Electric Co, Milwaukee, WI, USA.

^d Methadone Hydrochloride; Akorn, Inc, Lake Forest, IL, USA.

^e Midazolam Hydrochloride, Versed; Hospira, Lake Forest, IL, USA.

^f Ketamine Hydrochloride; Fort Dodge Animal Health, Fort Dodge, IA, USA.

^g Isoflurane USP, IsoFlo; Abbott Laboratories, IL, USA.

^h Fentanyl Citrate USP; Pfizer, NY, USA.

ⁱ Cefazolin; Westward Pharmaceutical, Eatontown, NJ, USA.

^j Rocuronium Bromide, Zemuron; Merck & Co. Inc., NJ, USA.

^k Jorgensen Laboratories, LLC, Loveland, CO, USA.

^l Surgical Simplex P; Stryker, Portage, MIm USA.

^m Smith & Nephew plc; Watford, United Kingdom.

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Publication History

Received: 08 February 2025

Accepted: 15 May 2025

Article published online:
20 June 2025